Installs the Lightpanda binary into a version-stamped
.browsers/lightpanda/<target>-<release>/ dir (mirroring Chrome's
.browsers/chrome/<target>-<version>/ layout so releases coexist) and
records the binary path in .browsers/PATHS.
Leaves any existing CHROME= entry in PATHS untouched.
The Lightpanda release is baked into the lightpanda dependency; bump
the dep to upgrade it.
Usage
mix wallabidi.install.lightpanda